Spotting

I am 12 weeks pregnant and a few days a go i started spotting a little. I went to the hospital and everything with the baby was fine. That day I went to my normal ultrasound and the baby looks perfect. I stopped spotting for 2 days and now it seems like the brown spotting is back. It only happens in the morning. I haven't had sex. I am not sure if it is an infection or not because I haven't gotten my results back yet. Anything to put my mind at ease? I have a fetal doppler and the baby still has a high heart beat. It sometimes burns when I pee.